Method of making a multi-channel magnetic head

ABSTRACT

A method of making a multi-channel magnetic head composed of a stack of a plurality of single-turn elementary heads. The method includes the step of defining a hollow for a conductive rod, which hollow extends through bore portions in core pieces and is open to each of a plurality of slots into which conductor plates are eventually placed to form with the conductive rod the single turns. The hollow is defined by the steps of inserting a hollowdefining rod of a heat resistant material into the bore portions and through first slots in a unitary body of magnetic oxide material; filling the bore portions and first slots with molten glass; cooling the molten glass; and cutting second slots at positions corresponding to the positions of the first slots. The conductive rod is then inserted, either after withdrawal of the hollow-defining rod where the hollow-defining rod is solid, or through the hollow defining rod where the hollow-defining rod is hollow. By this method, the combination of glass and the conventional conductive rod such as copper and solder becomes possible in a multi-channel magnetic head made up of a stack of a plurality of single-turn elementary heads, resulting in: long life of the resultant head because of the use of glass; low cost because of the use of an inexpensive conductive rod; very little cross-talk between adjacent channels; and high track density because of the use of a stack of a plurality of single-turn elementary heads.

United States Patent [1 1 Fujimura et al.

[ June 18, 1974 METHOD OF MAKING A MULTI-CHANNEL MAGNETIC HEAD [75] Inventors: Kenichi Fujimura; Takashi Tanaka,

both of Osaka, Japan [73] Assignee: Matsushita Electric Industrial Co.,

Ltd., Osaka, Japan [22] Filed: May 9, 1973 [2]] App]. No.: 358,609

[52] US. Cl. 29/603, 179/1002 C [51] Int. Cl ..Gl1b 5/42, l-lOlf 7/06 [58] Field of Search 29/603; 179/1002 C; 340/174.1 F; 346/74 MC [56] References Cited UNITED STATES PATENTS 3,402,463 9/1968 Bos et al. 29/603 3,518,646 6/1970 Sakasegawa 340/l74.l F 3,737,991 6/1973 Fujimura et al. 29/603 Primary Examiner-Charles W. Lanham Assistant Examiner-Carl E. Hall Attorney, Agent, or Firm-Wenderoth, Lind & Ponack [57] ABSTRACT A method of making a multi-channel magnetic head composed of a stack of a plurality of single-turn elementary heads. The method includes the step of defining a hollow for a conductive rod, which hollow extends through bore portions in core pieces and is open to each of a plurality of slots into which conductor plates are eventually placed to form with the conductive rod the single turns. The hollow is defined by the steps of inserting a hollow-defining rod of a heat resistant material into the bore portions and through first slots in a unitary body of magnetic oxide material; filling the bore portions and first slots with molten glass; cooling the molten glass; and cutting second slots at positions corresponding to the positions of the first slots. The conductive rod is then inserted, either after withdrawal of the hollow-defining rod where the hollow-defining rod is solid, or through the hollow defining rod where the hollow-defining rod is hollow. By this method, the combination of glass and the conventional conductive rod such as copper and solder becomes possible in a multi-channel magnetic head made up of a stack of a plurality of single-turn elementary heads, resulting in: long life of the resultant head because of the use of glass; low cost because of the use of an inexpensive conductive rod; very little cross-talk between adjacent channels; and high track density because of the use of a stack of a plurality of single-turn elementary heads.

16 Claims, 11 Drawing Figures METHOD OF MAKING A MULTl-CHANNEL MAGNETIC HEAD This invention relates to a method of making a multichannel magnetic head comprising a stack of a plurality of single-turn elementary heads.

A conventional multi-channel magnetic head with cores of magnetic metal such as permalloy is prepared e.g., in the following way. C-shaped core members or C-shaped and l-shaped core members having windings with a plurality of turns thereon are alternately stacked with a suitable space between adjacent core members in order to form a half of a multi-channel magnetic head. Then, two such halves of a multi-channel magnetic head are joined together with a spacer therebetween. Each of the core members in one half matches up with a corresponding core member in the other half in order to form an elementary head of the ring type.

A conventional multi-channel magnetic head with cores of a magnetic oxide such as a ferrite is prepared e.g., in the following way. Head tips are assembled into one stack in a manner such that each of the head tips has a thin layer of glass sandwiched between two magnetic parts. Two adjacent head tips are magnetically separated by a non-magnetic material. A plurality of magnetic head tips are joined with a plurality of magnetic back cores, each having a winding of a plurality of turns. One advantage of this multi-channel magnetic head is its long life because of the use of the combination use of magnetic oxide and glass.

In these conventional multi-channel magnetic heads, however, it is difficult to reduce the distance between two adjacent elementary heads because windings occupy a large space, resulting in low track density. Moreover, windings with a plurality of turns require large cores and cause high cross-talk between adjacent channels. Besides, in the case of the conventional multi-channel magnetic head with cores of a magnetic oxide, air gaps between head tips and back cores reduce output voltage and increase crosstalk. In the conventional multi-channel magnetic heads, one elementary head is apt to have an output voltage different from that of another because the elementary head is apt to have an air gap length different from that of another. The difference in the output voltage between elemen tary heads is a serious problem especiably in the case of a multi-channel magnetic head with small track widths, because it is difficult to eliminate the difference in the output voltage when the area between a back core and a corresponding head tip is small.

In order to eliminate these disadvantages, the applicants have already suggested, in the applicants earlier patent application Ser. No. 170,875 filed Aug. 1 1, 1971, now U.S. Pat. No. 3,737,991, a method of making a multi-channel magnetic head comprising a stack of a plurality of single-turn elementary heads. The method comprises the steps of:

grooving a flat surface of each of two blocks of magnetic oxide so as to leave a pair of shoulders on the opposite sides of said groove, said pair of shoulders being straight and parallel to each other, the flat surface of each of said pair of shoulders being smoothly polished, the fiat surface of one of said joining said two blocks to each. other into a unitary body with each pair of the joint surfaces, the grooves and the gap defining surfaces opposed to each other and with a gap between the pair of gap defining surface, said gap being filled with glass, and the pair of grooves defining a bore thereby;

inserting a conductive rod into said bore;

cutting plural slots in said unitary body in a direction perpendicular to the length of said bore, so as to leave plural core pieces each having therein a portion of the bore and to divide said conductive rod into a plurality of portions each of which remains within a corresponding portion of the bore, each of said core pieces having a width corresponding to the track width on a tape, and each of said slots having a width corresponding "to the space between adjacent tracks on a tape;

inserting two conductive plates into each of said slots and into electrical contact with the ends of the portions of said conductive rod exposed in the slots so as to form single-turn windings;

filling said slots with an adhesive material;

cutting the resultant composite body at a plane between said bore and the bottoms of said slots so as to form a stack of a plurality of single-turn elementary heads separated from each other by said adhesive material.

In this method, however, the resultant multi-channel magnetic head does not have satisfactory resistance to 0 wear because an adhesive material is used, resulting in unsatisfactory life of the head. If glass, which has high resistance to wear, could be used instead of the adhesive material in such method, the: problem of unsatisfactory life of the head would be solved. However, molten metal heated at e.g., 900 C) reacts with a conductive rod made of a conventional and inexpensive material such as copper. lf e.g., platinum is used as a material for the conductive rod, molten glass can be used, because molten glass does not react with platinum. However, the disadvantage is that platinum is very expensive.

The object of this invention is to provide a method of making a multi-channel magnetic head comprising a stack of a plurality of single-turn elementary heads such as those disclosed in applicants earlier patent application, in which molten glass can be used and a conventional and inexpensive conductive material which may react with glass at a high temperature e.g., 900 C) can be used for the conductive rod in order to obtain a multi-channel magnetic head having many advantages such as long life, high track density, small cores, little cross-talk and no difference in the output voltage between elementary heads.

This object is achieved by a method comprising the steps of:

l. grooving a flat surface of each of two blocks of magnetic oxide so as to leave a pair of shoulders on the opposite sides of said groove, said pair of shoulders being straight and parallel to each other, the flat surface of each of said pair of shoulders being smoothly polished, the flat surface of one of said pair of shoulders being a gap defining surface, and the flat surface of the other shoulder being a joint surface;

2. joining said two blocks to each other into a unitary body with each pair of the joint surfaces, the grooves and the gap defining surfaces opposed to each other and with a gap between the pair of gap defining surfaces, said gap being filled with glass, and the pair of grooves defining a bore thereby;

3. cutting a plurality of first slots in said unitary body in a direction perpendicular to the length of said bore from the outside surface of said unitary body to which said joint surfaces extend, so as to leave a plurality of core pieces each having therein a portion of said bore, the bottom of each of said first slots being located between said bore and the outside surface of said body to which said gap extends, each of said core pieces having a width corresponding to the track width on a tape, and each of said first slots having a width corresponding to the space between adjacent tracks on a tape;

4. defining a hollow for a conductive rod by inserting a hollow-defining rod of a heat resistant material through the portions of the bore and through said first slots; filling said portions of said bores and said first slots around said hollow-defining rod with molten glass; cooling the molten glass; and cutting second slots at positions corresponding to the positions of said first slots, said second slots extending through said hollow-defining rod;

5. forming a plurality of single-tum windings by inserting a conductive rod into said hollow and two conductive plates into each of said second slots, said two conductive plates separately being in electrical contact with the portions of said conductive rod in said second slots; and

6. cutting the resultant composite body at a plane between said bore and the bottom of each of said first slots so as to form a stack of a plurality of singleturn elementary heads separated from each other by said glass.

This object and other features of this invention will become apparent from the following detailed description taken together with the accompanying drawings, in which:

FIGS. 1 and 2 are perspective views showing the relationships of parts after the first few steps in one embodiment of a method of making a multi-channel magnetic head according to this invention;

FIGS. 3 and 4 are cross-sectional views showing the parts after further steps in the one embodiment of a method of making a multi-channel magnetic head according to this invention;

FIG. 5 is a perspective view showing the parts after a few steps in another embodiment of the method of making a multi-channel magnetic head according to this invention;

FIG. 6 is a side view showing the parts near the end of the one embodiment of a method of making a multichannel magnetic head according to this invention;

FIGS. 7, 8, 9 and 10 are perspective views of some conductive plates usable for the method of making a multi-channel magnetic head according to this invention; and

FIG. 11 is a front view showing the case when the conductive plates shown in FIG. 10 are used.

Referring to FIG. 1, reference numerals l and 2 designate blocks made of a magnetic oxide such as Mn-Zn ferrite and Ni-Zn ferrite. By grooving a flat surface of each of the two blocks 1 and 2 in a known manner, grooves 5 and 6 and four shoulders are made. Three of these shoulders are shown at 8,9 and 10. The shoulders have flat surfaces 3 and 4 smoothly polished. The surfaces 3 and 4 can be called the joint surface and gap defining surface, respectively, in view of the following joining step. The blocks are joined together into a unitary body with each pair of the joint surfaces 3 opposed to each other, and with the grooves 5 and 6 opposed to each other and with the gap defining surfaces 4 opposed to each other, whereby a gap 16 (as shown in FIG. 2) is defined between the gap defining surfaces 4, said gap 16 being filled with glass. The glass can be filled therein by any available and suitable manner, e.g., by filling molten glass (heated at e.g., 900 C) and cooling it or by depositing glass particles on the gap defining surface prior to joining to the other gap surface, heating it and cooling it. The grooves 5 and 6 opposed to each. other define a bore 13 (as shown in FIG. 2) thereby.

Referring to FIG. 2, reference numerals 17 and 16 designate a bore end and an outside end of the gap 15. In the unitary body, a plurality of first slots 11 are cut in a direction perpendicular to the length of the bore and extending into the body from an outside surface 19 of the unitary body to which the joint surfaces extend, so as to leave a plurality of core pieces 12. Any available and suitable method can be used for cutting the first slots. The bore 13 is also cut by the first slot cutting step into a plurality of bore portions, each of which is located in a core piece 12. One end 21 of each of the core pieces has a width W, corresponding to the track width on a tape. Each of the first slots 11 has a width W corresponding to the space between adjacent tracks on a tape. Reference numeral 18 designates a bore end of the joint surfaces. After the first slot cutting step, a hollow in which a conductive rod will be inserted afterwards is defined in either one of the following two manners.

In one manner, hollow-defining rod 14 made of a heat resistant material is inserted into the portions of the bore and through the first slots 11 in a direction perpendicular to the length of the first slots 11 as shown in FIG. 2. Then, the portions of the bore and the first slots 11 around the rod 14 are filled with molten glass 22 (as shown in FIG. 3) heated at e.g., 900C. The molten glass is cooled. The position of the hollowdefining rod substantially corresponds to the resultant and desired hollow and will be used for accommodating a conductive rod therein. Accordingly, all the requirements which it is necessary for the hollow-defining rod 14 to have are that the hollow-defining rod 14 does not react with molten glass at a high temperature such as 900 C and that it can define a hollow corresponding thereto, i.e., the glass 22 does not occupy the space occupied by the hollow-defining rod 14, and that the hollow-defining rod is easy to remove after defining the desired hollow. For example, mica, carbon and bamboo can be used as a material for the hollow-defining rod 17. Among the three materials, mica is best. The meaning of the expression heat resistant material as set forth above should be understood in view of the requirements as explained above. After the glass filling step, second slots 11' (as shown in FIG. 4) extending to but not extending beyond the bottom of the hollowdefining rod are cut at positions corresponding to the positions of the first slots from the outside surface of the unitary body to which the joint surfaces extend, so that any conductive plates and a conductive rod which will be inserted afterwards can be in electrical contact with each other at each of the second slots 11'. Thereafter, the hollow-defining rod is removed as shown in FIG. 4. Thus, bore portions 24 are also formed in core pieces 12'. FIG. 4 shows the case in which the width W of each of the second slots is substantially the same as the width W of each of the first slots. However, W can be larger or smaller than W This is why reference numerals 11' and 12 are used in FIG. 4 instead of 11 and 12. Also, the depth of the second slots can be imprecise, and the location of the bottom of each of the second slots can be imprecise, because the second slots are cut merely to form place into which conductive plates will be inserted so as to be in electrical contact with the conductive rod which will be inserted afterwards. When very low resistance of resultant single-turns is required, it be preferred that W is larger than W so as to make it possible to insert thicker conductive plates in the second slots afterwards. For the same reason, it is preferred that the conductive rod which will be inserted afterwards have a larger cross section.

If necessary, a shield plate 23 can be inserted, before the glass filling step, into each of the first slots between the surface of the hollow-defining rod facing the gap and the bottom of each of the first slots as shown in FIGS. 3, 4 and 6. In the vicinity of the gap (near the bore end of the gap), magnetic potential is high during play-back of a tape. Therefore, the shield plates 23, if inserted, are very advantageous.

One manner of defining a hollow for a conductive rod to be inserted afterwards (which hollow extends through the bore portions and is open to each of the second slots on one side thereof opposite to the side thereof toward the gap) has been described hereinbefore.

The other manner is essentially the same as said one manner and is a modification of said one manner.

According to the other manner, the hollow-defining rod 14 has a hollow therein. That is, according to the other manner, a hollow-defining rod 25 having a hollow interior 26 therein as shown in FIG. 5 is used as the ho]- low-defining rod. Accordingly, it is not necessary to remove the hoIlow-defining rod 25, because a conductive rod can be inserted into the hollow interior 26 of the hollow-defining rod 25. The hollow-defining rod is inserted into the bore portions and through the first slots; the bore portions and the first slots are filled with molten glass; and the molten glass is cooled and second slots are cut at positions of the first slots, the second slots extending through the hollow-defining rod. These steps are carried out in the same manner as in said one manner. In the case where the desired hollow is defined without removing the hollow-defining rod before the step of inserting a conductive rod in the hollow, it is very preferable that the material of the hollow-defining rod be stable at a high temperature (e.g., 900 C). For example, ceramic materials and platinum can be used as materials for the hollow-defining rod. So long as an inexpensive material such as copper is used as the material for the conductive rod, the use of platinum does not cause the method to be outside the scope of this invention, in spite of the statement in the introductory part of this specification which states that it is not necessary to employ an expensive material such as platinum for the conductive rod according to this invention. It is preferred that the thermal expansion coefficient of these materials for the hollow-defining rod 25 be similar to those of the core material (magnetic oxide) and the glass used.

It is clear that the principle of said one manner is the same as that of the other in that both manners define a hollow for a conductive rod to be inserted afterwards, which hollow extends through the bore portions and is open to each of the second slots at one side thereof opposite to the side thereof toward the gap.

After the hollow is defined, a conductive rod 27 is inserted into the defined hollow as shown in FIG. 6 in which the defined hollow is formed by the said one manner.

Any suitable material can be used for the conductive rod. According to this invention, even a material which reacts with molten glass at high temperature can be used. For example, copper, solder, phosphor bronze, iron and aluminum can be used. Copper and solder are more preferable than the others.

Two conductive plates 29 (as shown in FIG. 7) are inserted into each of the second slots 11 and separately are brought into electrical contact with the conductive rod 27 as shown in FIG. 6. At the opposite ends of the unitary body conductive plates 30 are provided which are in electrical contact with the conductive rod. Thus, two conductive plates 29 (or 30) on both sides of each core piece and one portion of the conductive rod 27 extending between the positions of the conductive plates form a single-turn winding. Any available and suitable material can be used for the conductive plates 29. If necessary, a shield plate 28 can be inserted between two conductive plates in each of the second slots 11.

If shield plate 28 is made of magnetic material such as ferrite, the shield plates not only reduce cross-talk between adjacent elementary heads, but also each insulates two conductive plates from each other in each of the second slots. In inserting the conductive rod and the conductive plates, material such as resin can be used to fill the space in the bore portions and the second slots other than the space occupied by the conductive rod and the conductive plates.

Instead of using conductive plates such as shown in FIG. 7, conductive plates as shown in FIGS. 8, 9 and 10 can be used. FIGS. 8 and 9 show conductive plates having recesses 32 at one (lower) side thereof so as to sit astride the conductive rod 20. The recesses 32 fix the position of the conductive plates 29 and make it easy to build up the multi-channel magnetic head. If a shield plate 28 is used, the shield plate also has a recess 32. The conductive plates shown in FIG. 9 are useful in e.g., a stagger arrangement of a transformer. The conductive plates shown in FIG. 10 have a hole 33 through which the conductive rod is to extend. If the conductive plates as shown in FIG. 10 are used, the conductive plates should be inserted into the: second slots before the conductive rod is inserted. FIG. 11 shows the ar rangement in which the conductive rod is inserted through the conductive plates of FIG. 10. The advantage of the use of the conductive plates of FIG. 10 is that the conductive rod can be secured firmly to the conductive plates so that the conductive plates and the conductive rod can be connected securely.

After the single-tum winding forming step, the resultant composite body 31 is cut at a plane 20 (as shown in FIGS. 2, 3, 4, 5 and 6) between the bore bottom of the gap and the end of each of the first slots so as to form a plurality of single-turn elementary heads separated from each other by said glass. This cutting process can be achieved by any available and suitable method.

Each of the elementary heads thus made has very small impedance and output, and requires very high recording current. Therefore, usually, a transformer is connected between each of the elementary heads and an amplifier for matching the impedance and for trans forming voltage and current.

Each of the elementary heads thus made has a smaller size than the conventional heads. Therefore, cross-talk between adjacent channels is much smaller.

By the above-mentioned method of making a multichannel magnetic head, the resultant multi-channel magnetic head can have very short distance between adjacent elementary heads. Moreover, each elementary head of the resultant multi-channel magnetic head has a high output compared with conventional heads. One elementary head has an output nearly equal to that of the others. This is because each elementary head core does not have joints between the head tip and the back core. Heads without such joints produce much less cross-talk between adjacent elementary heads than those with such joints.

Furthermore, because the tape engaging surface of the resultant head according to this invention is composed of glass and magnetic oxide such as a ferrite material, the head has high resistance to wear and long life. The resultant single-turn windings can have very low electrical resistance. The electrical resistance is further lowered because the conductive rod and the conductive plates occupy more of the space of the bore portions and the second slots. When a step-up transformer is used to step up the head voltage in a playback process, the lower limit of the frequency range is a frequency at which the inductive impedance of the primary winding of the transformer is nearly equal to the total resistance of the head and transformer windings. The lower limit of the frequency range is low because the electrical resistance of the resultant singleturn windings is low.

Because the magnetic oxide material has high resistivity, insulation between the conductive rod or conductive plates and the core is not necessary.

Lastly, it should be noted that the conductive rod and the conductive plates can be more easily and more completely connected by using one of the following methods.

According to one method, the two conductive plates in each of the second slots are separated by an insulating sheet such as mica, and then the second slots are filled with electrically conductive adhesive, such as solder and silver paint. When a magnetic plate 28 sandwiched between two conductive plates is used and is made of material having high resistivity such as ferrite, it can act as the insulating sheet.

Another method is one in which the conductive rod and/or the conductive plates are made of solder and are connected together by heating.

Still another method is the conductive rod and/or the conductive plates 22 are covered with a solder layer and heated for solder connection.

What we claim is:

l. A method of making a multi-channel magnetic head, comprising the steps of:

l. grooving a fiat surface of each of two blocks of magnetic oxide to form a groove and to leave a pair of shoulders on each block with the individual shoulders of the pair on the opposite sides of said groove. said pair of shoulders being flat and parallel to each other, the flat surface of each of said pair of shoulders being smoothly polished, the flat surface of one of said pair of shoulders being a gap defining surface, and the flat surface of the other shoulder being a joint surface;

2. joining said two blocks to each other into a unitary body with each pair of the joint surfaces, the grooves and the gap defining surfaces opposed to each other and with a gap between the pair of gap defining surfaces, said gap being filled with glass, and the pair of grooves defining a bore extending longitudinally through said unitary body;

3. cutting a plurality of first slots in said unitary body in a direction perpendicular to the length of said bore and extending into said body from the outside surface thereof to which said joint surfaces extend, so as to leave a plurality of core pieces each having a bore portion therein, the bottom of each of said first slots being located between a bore end and an outside end of said gap, each of said core pieces having a width corresponding to the track width on a tape, and each of said first slots having a width corresponding to the space between adjacent tracks on a tape;

4. defining a hollow for a conductive rod by the steps including: inserting a hollow-defining rod of a heat resistant material into the bore portions and through said first slots; filling the portions of said bore portions and said first slots not occupied by and exterior to the outer perimeter of said hollowdefining rod with molten glass; cooling the molten glass; and cutting second slots at positions corresponding to the positions of said first slots, said second slots extending through the position said hollow-defining rod occupies when it is in the bore portions and first slots;

5. forming a plurality of single-turn windings by inserting a conductive rod into the hollow defined by said hollow-defining rod and two conductive plates into each of said second slots, said two conductive plates separately being in electrical contact with said conductive rod; and

6. cutting the resultant composite body at a plane between said bore end of said gap and the bottom of each of said first slots so as to form a stack of a plurality of single-turn elementary heads separated from each other by said glass.

2. A method according to claim 1, wherein the steps of defining said hollow includes removing said hollowdefining rod from said bore portions and said second slots before the step of inserting a conductive rod into said hollow, whereby the space occupied by said hollow-defining rod in the unitary body corresponds to said hollow.

3. A method according to claim 2, wherein said hollow-defining rod is made of one member selected from the group consisting of mica, carbon and bamboo.

4. A method according to claim 1, wherein the step of inserting a hollow-defining rod comprises inserting a rod having a hollow therein which corresponds to said hollow to be defined.

5. A method according to claim 4, wherein said hollow-defining rod is made of a member selected from the group consisting of a ceramic material and platinum.

6. A method according to claim 1, wherein the step of cutting said second slots comprises cutting slots having widths similar to that of the corresponding first slots.

7. A method according to claim 1, wherein the step of cutting said second slots comprises cutting slots having widths larger than that of the corresponding first slots.

8. A method according to claim 1, wherein the step of cutting said second slots comprises cutting slots having widths smaller than that of the corresponding first slots.

9. A method according to claim 1, wherein a shield plate is inserted into each of said first slots between the side of said hollow-defining rod facing said gap and the bottom of each of said first slots, the direction of the length of said shield plate being parallel with the direction of said first slots.

10. A method according to claim 1, wherein said conductive plates have recesses in one side thereof so as to sit astride said conductive rod.

11. A method according to claim 1, wherein each of said conductive plates has a hole through which said conductive rod extends, and said conductive plates are positioned in said second slots and thereafter said conductive rod is inserted into said hollow.

12. A method according to claim 1, wherein a magnetic plate is positioned between said two conductive plates in each of said second slots.

13. A method according to claim 1, wherein insulating material is positioned between said two conductive plates in each of said second slots, and each of said second slots is filled by an adhesive material having electrical conductivity for placing said two conductive plates in electrical contact with said conductive rod.

14. A method according to claim 1, wherein at least one of said conductive rod and said conductive plates are made of solder, and the step of inserting said conductive rod and said plates includes heating them for placing them in electrical connection with each other by soldering.

15. A method according to claim 1, wherein at least one of said conductive rod and said conductive plates are covered with solder, and the step of inserting said conductive rod and said plates includes heating them for placing them in electrical connection with each other by soldering.

16. A method according to claim 1, wherein said conductive rod is made of a member selected from the group consisting of copper and solder. 

1. A method of making a multi-channel magnetic head, comprising the steps of:
 1. grooving a flat surface of each of two blocks of magnetic oxide to form a groove and to leave a pair of shoulders on each block with the individual shoulders of the pair on the opposite sides of said groove, said pair of shoulders being flat and parallel to each other, the flat surface of each of said pair of shoulders being smoothly polished, the flat surface of one of said pair of shoulders being a gap defining surface, and the flat surface of the other shoulder being a joint surface;
 2. joining said two blocks to each other into a unitary body with each pair of the joint surfaces, the grooves and the gap defining surfaces opposed to each other and with a gap between the pair of gap defining surfaces, said gap being filled with glass, and the pair of grooves defining a bore extending longitudinally through said unitary body;
 3. cutting a plurality of first slots in said unitary body in a direction perpendicular to the length of said bore and extending into said body from the outside surface thereof to which said joint surfaces extend, so as to leave a plurality of core pieces each having a bore portion therein, the bottom of each of said first slots being located between a bore end and an outside end of said gap, each of said core pieces having a width corresponding to the track width on a tape, and each of said first slots having a width corresponding to the space between adjacent tracks on a tape;
 4. defining a hollow for a conductive rod by the steps including: inserting a hollow-defining rod of a heat resistant material into the bore portions and through said first slots; filling the portions of said bore portions and said first slots not occupied by and exterior to the outer perimeter of said hollow-defining rod with molten glass; cooling the molten glass; and cutting second slots at positions corresponding to the positions of said first slots, said second slots extending through the position said hollow-defining rod occupies when it is in the bore portions and first slots;
 5. forming a plurality of single-turn windings by inserting a condUctive rod into the hollow defined by said hollow-defining rod and two conductive plates into each of said second slots, said two conductive plates separately being in electrical contact with said conductive rod; and
 6. cutting the resultant composite body at a plane between said bore end of said gap and the bottom of each of said first slots so as to form a stack of a plurality of single-turn elementary heads separated from each other by said glass.
 2. joining said two blocks to each other into a unitary body with each pair of the joint surfaces, the grooves and the gap defining surfaces opposed to each other and with a gap between the pair of gap defining surfaces, said gap being filled with glass, and the pair of grooves defining a bore extending longitudinally through said unitary body;
 2. A method according to claim 1, wherein the steps of defining said hollow includes removing said hollow-defining rod from said bore portions and said second slots before the step of inserting a conductive rod into said hollow, whereby the space occupied by said hollow-defining rod in the unitary body corresponds to said hollow.
 3. A method according to claim 2, wherein said hollow-defining rod is made of one member selected from the group consisting of mica, carbon and bamboo.
 3. cutting a plurality of first slots in said unitary body in a direction perpendicular to the length of said bore and extending into said body from the outside surface thereof to which said joint surfaces extend, so as to leave a plurality of core pieces each having a bore portion therein, the bottom of each of said first slots being located between a bore end and an outside end of said gap, each of said core pieces having a width corresponding to the track width on a tape, and each of said first slots having a width corresponding to the space between adjacent tracks on a tape;
 4. defining a hollow for a conductive rod by the steps including: inserting a hollow-defining rod of a heat resistant material into the bore portions and through said first slots; filling the portions of said bore portions and said first slots not occupied by and exterior to the outer perimeter of said hollow-defining rod with molten glass; cooling the molten glass; and cutting second slots at positions corresponding to the positions of said first slots, said second slots extending through the position said hollow-defining rod occupies when it is in the bore portions and first slots;
 4. A method according to claim 1, wherein the step of inserting a hollow-defining rod comprises inserting a rod having a hollow therein which corresponds to said hollow to be defined.
 5. A method according to claim 4, wherein said hollow-defining rod is made of a member selected from the group consisting of a ceramic material and platinum.
 5. forming a plurality of single-turn windings by inserting a condUctive rod into the hollow defined by said hollow-defining rod and two conductive plates into each of said second slots, said two conductive plates separately being in electrical contact with said conductive rod; and
 6. cutting the resultant composite body at a plane between said bore end of said gap and the bottom of each of said first slots so as to form a stack of a plurality of single-turn elementary heads separated from each other by said glass.
 6. A method according to claim 1, wherein the step of cutting said second slots comprises cutting slots having widths similar to that of the corresponding first slots.
 7. A method according to claim 1, wherein the step of cutting said second slots comprises cutting slots having widths larger than that of the corresponding first slots.
 8. A method according to claim 1, wherein the step of cutting said second slots comprises cutting slots having widths smaller than that of the corresponding first slots.
 9. A method according to claim 1, wherein a shield plate is inserted into each of said first slots between the side of said hollow-defining rod facing said gap and the bottom of each of said first slots, the direction of the length of said shield plate being parallel with the direction of said first slots.
 10. A method according to claim 1, wherein said conductive plates have recesses in one side thereof so as to sit astride said conductive rod.
 11. A method according to claim 1, wherein each of said conductive plates has a hole through which said conductive rod extends, and said conductive plates are positioned in said second slots and thereafter said conductive rod is inserted into said hollow.
 12. A method according to claim 1, wherein a magnetic plate is positioned between said two conductive plates in each of said second slots.
 13. A method according to claim 1, wherein insulating material is positioned between said two conductive plates in each of said second slots, and each of said second slots is filled by an adhesive material having electrical conductivity for placing said two conductive plates in electrical contact with said conductive rod.
 14. A method according to claim 1, wherein at least one of said conductive rod and said conductive plates are made of solder, and the step of inserting said conductive rod and said plates includes heating them for placing them in electrical connection with each other by soldering.
 15. A method according to claim 1, wherein at least one of said conductive rod and said conductive plates are covered with solder, and the step of inserting said conductive rod and said plates includes heating them for placing them in electrical connection with each other by soldering.
 16. A method according to claim 1, wherein said conductive rod is made of a member selected from the group consisting of copper and solder. 